Tim, That's a thought. But even still the nature of Daub is high maintenance. The difficulty lies not only in the fact that it shrinks as it dries, but that the formation of frost within causes the molecular structure to break down over time -the same affect that you use to your advantage when making any loam wall material as you leave the dirt to sit out in small piles over the winter so that the frost can break it down.

To alleviate this problem, clay bricks rely on the addition of sand and other aggregates. And many times the Loam wall systems are mostly straw and have very little actual clay in them. (This is not only true of the modern Lehmbau, but also of older techniques dating back to the middle ages)

About the issue of bracing on the bohlenwand:
The Bohlenwand is a major part of the Swiss tradition. In Switzerland the general practice is to have the planks sit flush with the inside of the wall, and the braces are then let in from the outside. These braces rely on lap dovetail joints. Alternately the planks are set in the middle, and thin braces are let in on both the inside and outside.

Example:


That image is from a very good book, the part covering Bohlenwand can be found here:
http://durm.semanticsoftware.info/wiki/index.php/Durm:Bohlenw%C3%A4nde

Browse through that book, It's incredible. Great pictures that show a lot.

Obviously let in braces will not work if the board are 3/4 of an inch from the edges of the timbers.

A possible solution, however, is to instead nail boards onto notches cut on the outside of the timbers (the timbers would have a cross section somewhat like a fat +) This would actually solve 3 problems at once, it makes it so that inserting the boards around braces and such is quite quick and easy, it makes it so that the boards can be inserted after the frame is raised, and it eliminates the problem of the floating boards moving relative to the top plate, which could cause serious plaster issues.